1. Technical Field
The present invention relates to a discharge lamp lighting device, a control method for the same, and a projector.
2. Related Art
As a light source of a projector, a discharge lamp such as a high-pressure mercury lamp or metal halide lamp is used. In such a discharge lamp, wear of electrodes due to discharge causes change in the shape of the electrodes. If plural protrusions are grown at the distal end of the electrodes or irregular wear of the electrode bodies progresses, shift of arc starting point and change in arc length occur. These phenomena cause reduction in luminance of the discharge lamp and shorten the life of the discharge lamp. This is not desirable.
As a method to address this problem, U.S. Pat. No. 6,815,907 proposes a technique of pulse width modulation with the absolute value of an AC current for discharge lamp driving maintained substantially at a constant level.
However, in the case where a discharge lamp is used to a projector the like, driving power may be changed by light adjustment or mode switching by the user (for example, switching between a high-luminance mode for high-power driving and a long-life mode for low-power driving). Since the temperature of the electrodes is proportional to power supplied to the discharge lamp, in the case of low-power driving, particular attentions must be paid in order to restrain occurrence of flicker when the electrode temperature is lowered.